Apparatus and process for drilling underground arcuate paths

ABSTRACT

An improved apparatus and process for drilling an inverted underground arcuate path is disclosed. A drill rig having an acute angle of attack from the horizontal is placed interiorally of a pit where it enters the ground typically normal to the sidewall of the pit. A drill string powering a motorized drill is urged downwardly into the ground by the drill rig. The drill at the drilling end of the drill string has a slight angle imparted thereto. As the drill string is urged into the ground and the drill is angularly aligned with respect to the string, an inverted arcuate path is bored by the drill so as to enter the ground downwardly and angularly at an entrance point and to exit the ground upwardly and angularly at an exit point with an inverted arcuate path therebetween. Parameters for controlling the arcuate path without withdrawing of the drill string to change drills or drill alignment are disclosed. Specifically, by slowing drill speed, increasing thrust on the drill string, and/or aligning the angularlity of the drill to vector upwardly the radius of curvature of the drill path can be decreased. Conversely, by increasing rotational drill speed, decreasing thrust on the drill string, or aligning the bend of the drill string to vector horizontally or downwardly, the radius of curvature of the inverted arcuate path can be increased.

United States Patent 1 1 Cherrington [451 Apr. 22, 1975 1 APPARATUS AND PROCESS FOR DRILLING UNDERGROUND. ARCUATE PATns [76] Inventor: Martin Dee Cherrington, 7398 San Joaquin St., Sacramento, Calif. 95825 221 Filed: Dec. 4, 1973 211 Appl. No.: 421,548

[52] US. Cl. 175/45; 175/61; 175/73;

Primary E.raminerFrank L. Abbott Assislant Eraminer-Richard E. Favreau Attorney, Agent, or Firm-Townsend and Townsend [57] ABSTRACT An improved apparatus and process for drilling an inverted underground arcuate path is disclosed. A drill rig having an acute angle of attack from the horizontal is placed interiorally of a pit where it enters the ground typically normal to the sidewall of the pit. A drill string powering a motorized drill is urged downwardly into the ground by the drill rig. The drill at the drilling end of the drill string has a slight angle imparted thereto. As the drill string is urged into the ground and the drill is angularly aligned with respect to the string, an inverted arcuate path is bored by the drill so as to enter the ground downwardly and angularly at an entrance point and to exit the ground upwardly and angularly at an exit point with an inverted arcuate path therebetween. Parameters for controlling the arcuate path without withdrawing of the drill string to change drills or drill alignment are disclosed. Specifically, by slowing drill speed, increasing thrust on the drill string, and/or aligning the angularlity of the drill to vector upwardly the radius of curvature of the drill path can be decreased. Conversely, by increasing rotational drill speed, decreasing thrust on the drill string, or aligning the: bend of the drill string to vector horizontally or downwardly, the radius of curvature of the inverted arcuate path can be increased.

22 Claims, 5 Drawing Figures PATEKHEU APR 2 21975 snmanrg APPARATUS AND PROCESS FOR DRILLING UNDERGROUND ARCUATE PATHS BACKGROUND OF THE INVENTION The present invention relates to drillinginverted underground arcuate paths from one surface point to another.

The traditional method for laying pipelines. telephone cables and other underground conduits is to dig an open trench. lay the conduit in the trench and then close the trench. This method is quite efficient in gen eral. but problems arise when an obstacle such as a water course or a heavily traveled road is encountered. and the conduit must traverse the obstacle.

When a road is encountered. the road must either be closed. the traffic diverted. or parts of the road closed and the conduit laid in sections. all of which are inconvenient and interfere substantially with the use of the road. When a conduit must span a water course. other problems arise. First. the trench must be dug to a depth considerably below the level at which the conduit is to be laid since the current will partially fill the trench before the conduit can be inserted. This is a significant problem because such trenches have a generally triangular cross section. and the volume of dirt which must be removed increases with the square of the depth of the trench. Such trenching also stirs the alluviuni at the bottom of the water course interfering with the natural flora.

Even after a trench has been dug in a water course. difficulties arise in placing the conduit therein. One method of placing the conduit is to float it across the span of the water course and then remove its buoyancy to sink the pipe into the trench. The difficulty with this method is that the water course must be closed to traffic. floating objects are trapped by the floating conduit. the current of the river bends the conduit. and when the conduit is sunk. it quite often misses the trench. A second method is to attach a sled or skid to the leading end of the conduit. and drag this leading end through the trench to lay the conduit. With this method. the conduit must be coated with a substance to give it negative buoyancy. and this coating is quite expensive since the entire length of the conduit must be so coated.

Traditional methods of digging wells cannot be adapted to digging arcuate paths such as that required for implacing a pipeline or other conduit under an obstacle. Such methods utilize a drill string which enters the ground substantially normal to its surface. and the path must undergo a 180 turn to span the obstacle. Such a path would result in the drill string extending vertically upwardly at the other side of the obstacle with the weight ofthe drill string acting against the forward motion of the drill. Since the weight of the string is used to drive the drill. such a method cannot be used.

Traditional well drilling methods rely on the weight of the pendant drill string to achieve a substantially vertical hole. When an angular bend in the hole was desired. it was formerly the practice to lower a whip stock shim into the bottom of the hole which forced the drill off at an angle. Later methods utilize a self-powered drill which has a drill stem slightly angularly inclined with respect to the drill string. The problem with both of these methods is that the entire drill string must be removed from the hole. either to lower the whip stock or to mount the inclined drill. After the angle has been made. the entire drill string must be withdrawn again to remove either the whip stock or the inclined drill. This is extremely time consuming and inefficient since drill strings may be many thousands of feet in length. Furthermore. these methods provide no means for controlling the bend along its length other than removing and replacing the drill string whenever a change in angle is desired. Hence. these methods are unacceptable for drilling controlled arcuate paths and can only be used for intermittent bends and/or constant radius turns.

Techniques have been developed for drilling holes along a substantially linear horizontal path for placing telephone lines under streets and the like. However. these methods employ drills which proceed in a straight line. and to achieve an arcuate path. a pothole must be dug and the drill manually redirected. Such a method is often acceptable in traversing obstructions such as a road, but cannot be used for traversing a water course because the required potholes cannot be dug.

SUMMARY OF THE INVENTION The present invention provides an apparatus and process for drilling an inverted underground arcuate path. A drill rig having an acute angle of attack from the horizontal is placed in teriorally of a pit where it enters the ground typically normal to the sidewall of the pit. A drill string powering a motorized drill is urged angularly downwardly into the ground by the drill rig. The drill at the drilling end of the drill string has imparted thereto an angle usually in the range of ll0 but possibly larger. As the drill string is urged-into the ground and the drill is angularly aligned with respect to the string. an inverted arcuate path is bored by the drill so as to enter the ground downwardly and angularly at an entrance point and to exit the ground upwardly and angularly at an exit point with an inverted arcuate path therebetween. Parameters for controlling the arcuate path without withdrawing of the drill string to change drills or drill alignment are disclosed. Specifically. by slowing drill speed. increasing thrust on the drill string. and/or aligning the angularity of the drill to vector upwardly the radius of curvature of the drill path can be decreased. Conversely. by increasing rotational drill speed. decreasing thrust on the drill string. or aligning the bend of the drill string to vector horizontally or downwardly. the radius of curvature of the inverted ar cuate path can be increased.

The present invention allows for drilling a hole beneath a surface obstacle to avoid the necessity of utilizing the standard trenching method for laying a conduit across the obstacle. When the obstacle is a road or water course. traffic along that obstacle is in no way impeded. Ecological disturbances such as interfering with the natural flora on a river bottom are minimized. The conduit can be placed far below the depth of the water course so that shifts in the water course will not expose it. Also. the entrance and exit points of the conduit can be far removed from the edge of the obstacle so that levies and natural shores need not be breached. Furthermore. all of the aforementioned difficulties associated with laying a pipe in a trench are eliminated.

The present invention provides means for controlling the course of the inverted underground arcuate hole as it is being drilled. The following parameters are utilized: thrust on the drill string. speed of the drill rotors. volume of drilling mud passed to the drill. and azimuth of the inclined drill bit. By manipulating these parameters. the pitch of the drill bit as it travels is controllable to allow the path of the drill bit to be selectively varied as the hole is being drilled. This allows for continuous drilling of the hole from the entrance to the exit. and eliminates the necessity for removing and replacing the drill bit or other apparatus. greatly reducing the time and expense required to drill the hole.

The novel features which are believed to be characteristic of the invention. both as to organization and method of operation, together with further objects and advantages thereof will be better understood from the following description considered in connection with the accompanying drawings in which a preferred embodiment of the invention is illustrated by way of example. It is to be expressly understood. however. that the drawings are for the purpose ofillustration and description only and are not intended as a definition of the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective schematic cross-section of the operation of the present invention in drilling an inverted arcuate hole under a water course:

FIG. 2 is a side elevation view of the inclined drill rig of the present invention.

FIG. 3 is a fragmentary side elevation section of the drill head utilized in the present invention:

FIG. 4 is a side elevation section illustrating the control over the drill head achieved by the present invention:

FIG. 5 is a plan section illustrating a different manner of control over the drill head of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The schematic view of FIG. 1 illustrates a water course having banks 12 and 14. A house 16 is located on bank 14. An underground inverted arcuate hole along path 18 passes from adjacent the surface on bank 12 to adjacent the surface on bank 14. A plurality of discrete survey points 20 are located along path 18. It should be noted that path 18 passes between the bot tom of water course 10 and a layer of shale 22. The arcuate hole 18 of FIG. 1 is formed by an inclined drill rig apparatus 24 located on bank 12 of water course 10. The hole is dug from its entrance point on bank 12 to an exit point on bank 14 past house 16 utilizing the method and apparatus of the present invention.

The inclined drill rig apparatus 24 of the present invention is illustrated in more detail by way of'reference to FIG. 2. Apparatus 24 includes ramp mounted to the ground 32 in a pit 34. Forward wall 36 of pit 34 is inclined with respect to horizontal 38 and is adapted to be normal to the slope of the inclined ramp 30. The appropriate angle of declination of ramp 30 is governed by the length and depth of the desired arcuate hole and is hence variable. Angles of declination from 5 to down from horizontal have been utilized in practice with the preferred range lying between l0 and 30 to achieve the desired control over the drill head. FIG. 2 illustrates a mid-range angle of declination from the horizontal of 22.

A power source 40 rides along ramp 30 on wheels 42. Movement of power source 40 along the ramp is controlled by the use of line 44 which dead ends at the extremeties of the ramp, but which wraps around a powered winch 46 on power source 40. Power source 40 is usually an internal combustion engine having a plurality of power take-off attachments. but a wide variety of power sources could be employed. Power source 40 is utilized to thrust the drill string 48 angularly downwardly into ground 50 as illustrated by arrow 52 by driving winch 46. Controls are provided for winch 46 to control the forward thrust on drill string 48. Drill string 48 comprises a plurality of drilling pipes as known in the oil well drilling art, and in fact. standard oil well. drilling materials are used to form the drill string. In the present invention, drill string 48 ordinarily does not rotate to operate the drill, but is rotatable in azimuth about its axis to control the drill head as will hereinafter be illustrated. Hence, power source 40 is capable of providing selective rotational control over the azimuth of drill string 48 as well as thrusting the drill string into the ground by means of winch 46.

Power source 40 is also adapted to force drilling mud through the hollow interior of drill string 48 to power the drill head and remove loosened particles from the drilled hole. A tube 54 from a source of such drilling mud (not shown) provides the drilling mud to power source 40. Drilling mud circulates down through the hollow interior of drill string 48 and then back around the exterior of the drill string and out of the drilled hole as illustrated by arrow 56 where it is dumped in the lower portion of pit 34. A certain amount of such mud 58 is allowed to collect in pit 34, but most of the mud is returned to its source through tube 60. The entrance to the drilled hole at face 36 of pit 34 is provided with a conduit 62 extending outwardly through face 36. Drilling mud exiting the drilled hole thus does not run down face 36 of pit 34 and erode the pit. allowing the pit to retain its preferred configuration.

FIG. 3 illustrates the attachment ofa drill head casing to the end 72 of drill string 48 opposite power source 40. Drill head 70 is of the type known in the art wherein the drilling mud forced through drill string 48 is used to power the drill. Drill head 70 is of the type which has an angular bend 74 with respect to the axis of drill string 48 so that the drill bit portion 76 of drill head 70 is angularly inclined as illustrated. The angular bend 74 of drill 70 can be varied. and inclinations of from 1 to 5 are well known in the art. However, it has been found advantageous in the present invention to increase the angular bend at least to 10 and possibly greater in many applications to achieve the desired control over its movement. The angular bend 74 shown in the figures is probably too large for most applications, however, and is probably an exaggeration. The upper bound of this parameter has yet to be determined. The cutting portion 78 of drill bit 76 is thus angled significantly with respect to drill string 48. Cutting tip 78 is-of the typeknown in the art and usually has three rotors each having a plurality of cutting teeth.

A surveying instrument 80 is adapted to slide through the hollow interior of drill string 48 to a position adjacent drill head 70. Surveying tools 80 known in the art are primarily of the single-shot variety, i.e., the tool takes a single reading and is then withdrawn through drill string 48 for assessment. Surveying instrument 80 ordinarily measures the azimuth and declination of the leading end 72 of drill string 48. This data together with the length of the string and a history of the drill path allow the current position of drill head 70 to be determined.

It should be noted by way of reference to FIG. 3 that the hole 82 dug by drill head 70 is curved along its length as a result of angular bend 74 in drilling head 70. Drilling head 70 rests on the bottom of hole 82 at position 92 below bend 74 when the drill head is vectored upwardly as illustrated. causing the curved path of hole. If the parameters on drill head 70 are maintained constant. hole 82 will have a constant upward curvature as illustrated by hole 82 in FIG. 4. However. the

apparatus of the present invention. as illustrated in FIG. 2, provides means for controlling the angularity-of the hole along its length and thus its eventual contour.

Specifically. the forward thrust on drill string 48 exerted by power source 40 through winch 46 can be increased. and such action will decrease the radius of curvature as illustrated by phantom hole 90. The apparent reason for this fact is that drill head 70 rests at two points. the bottom of the angular bend illustrated at 92. and the leading end of the hole illustrated at 94 in FIG. 4. Increasing the forward thrust on drill string will apparently force drill head 70 against position 94, reducing the gravitational load at position 92. thereby increasing the pitch (angle from horizontal) of drill head 70. Conversely. decreasing the forward thrust on drill string 48 exerted by power source 40 will increase the radius of curvature of the hole illustrated by the phantom hole 96.

A further control feature provided by the apparatus of the present invention is that the forcing of drilling mud through the interior of drill string 48 by power source 40 is controllable. Increasing the force on the drilling mud has two effects on the drill: first. the speed of the drill rotors on tip portion 78 is increased; and second. the volume of drilling mud expelled through tip 78 of drill head 70 is increased. This increase in the flow of drilling mud will result in increasing the radius of curvature of the hole as illustrated by phantom 96. Conversely. decreasing the flow will decrease the radius of curvature as illustrated by phantom 90. The exact mechanism of this phenomena is not fully understood. but it would appear that both the increase in the speed of rotation of tips 78 and the increase in the drilling mud flowing therethrough reduces the friction at point 94, resulting in a corresponding increase in the gravity effect at point 92. thereby increasing the radius of curvature of the path and vice versa.

A further control feature of the apparatus of the present invention is illustrated by way of reference to FIG. 5. Drilling head 70 is ordinarily positioned so that drill bit '76 is vectored upwardly. It is known that the azimuth of drill bit 70 can be altered by rotating drill string 48 to make horizontal turns in the drill path. However. the present invention provides the additional control of rocking drill head 70 from side to side as illustrated by arrows 98. 98 or in a full circle in rapid fashion. This will not result in a hole which corkscrews but rather will tend to increase the radius of curvature of the arcuate path without introducing a significant horizontal turn.

In operation. the apparatus of the present invention is utilized as follows. First a pit 34 is dug at one side of an obstruction which is to be traversed with a pipeline or other underground conduit. The forward surface 36 of the pit is inclined from the vertical at a preselected angle. The angle is dependent on the depth of cut desired and the width of the obstacle. A ramp is next placed in the pit. and has a lower end terminating at the forward face 36 thereof. Power source is mounted on ramp 30 and the drilling of the hole is initiated. Drillingof the hole can be begun with traditional straight line drilling methods. However. the control provided by the present invention allows for the preferred method of initiating drilling with the inclined drill head 70.

The apparatus of the present invention allows the drillhead to be directed in a controlled manner beneath the obstruction to surface at the other side. Controlling the thrust on drill string 48, the force of drilling mud into the drill string, and azimuth of the drill head all can be utilized to control the direction of the drilling. Hence. the present invention provides a method whereby a hole can be drilled continuously under an obstruction from one side to the other for the laying of the conduit.

Although a preferredembodiment of the present invention has been illustrated in. detail. it is apparent that modifications and adaptations of that embodiment will occur to those skilled in the art. In particular. the configuration of the drill rig apparatus can be varied. and different mechanisms employed to vary the control parameters of the present invention. However. it is to be expressly understood that such modifications and adaptations are within the spirit and scope of the present invention. as set forth in the following claims.

What I claim as new is:

1. A method for drilling underground an inverted arcuate path beneath an obstacle comprising the steps of: providing a drill string; providing a drill head having at least one cutting drill bit at the end of said drill string operative to cut independent of rotation of said drill string. said drill head having an angular axial alignment with respect to the axis of said drill string; thrusting the drill string angularly downward into the ground at an angle other than vertical; powering said drill bit through said drill string simultaneously with said thrusting step; surveying the azimuth and declination of said drill string proximate said drill head at a plurality of intervals during said drilling and measuring the length of said drill string in the ground at a correspondent plurality of intervals from entrance into the earth at one side of said obstacle to exit from the earth at the other side of said obstacle whereby the path of said drill under said obstacle can be determined; and. varying said thrust of said drill string to change the radius of curvature of said inverted arcuate path.

2. A method as recited in claim 1 wherein said varying said thrust includes increasing the force on said drill string to decrease the radius of curvature of the inverted arcuate path.

3. The method of claim 1 wherein said thrusting step includes decreasing the force on said drill string to increase the radius of curvature of the inverted arcuate path.

4. The method of claim 1 and varying the speed of said drill head to change the radius of curvature of said inverted arcuate path.

5. The method of claim 1 and wherein said powering step includes powering said drill head through said drill string by fluid supplied to a motor operatively connected to said drill bit, and including the step of varying the pressure of said fluid to said motor to change said radius of curvature. 1

6. The invention of claim I and including the step of rocking said drill head from side to side by turning said drill string to change the radius of curvature of said inverted arcuate path.

7. A method for drilling underground an inverted arcuate path beneath an obstacle comprising the steps of: providing a drill string; providing a drill head having at least one cutting drill bit at the end of said drill string operative to cut independent of rotation of said drill string; said drill head having an angular axial alignment with respect to the axis of said drill string; thrusting the drill string angularly downward into the ground at an angle other than vertical; powering said drill bit through said drill string simultaneously with said thrusting. step; surveying the azimuth and declination of said drill string proximate said drill head at a plurality of intervals during said drilling and measuring the length of said drill string in the ground at a correspondent plurality of intervals from entrance into the earth at one side of said obstacle to exit from the earth at the other side of said obstacle whereby the path of said drill under said obstacle can be determined; and. varying the speed of said drill bit to change the radius of curvature of said inverted arcuate path.

8. A method as described in claim 7 wherein said varying of the speed of said drill bit includes the step of increasing the rotational speed of said drill bit to increase the radius of curvature of said inverted arcuate path.

9. The method as described in claim 7 wherein said varying the speed of said drill bit includes the step of decreasing the rotational speed of said drill bit to decrease the radius of curvature of said inverted arcuate path.

10. The invention of claim 7 and including the step of varying the thrust of said drill string to change the radius of curvature of said inverted arcuate path.

11. The method of claim 7 and including the steps of powering said drill head by fluid communicated through said drill string to a motor operatively connected to said drill bit and controlling the radius of curvature of said inverted arcuate path by varying the pressure of said fluid.

12. The invention of claim 7 and including the step of rocking said drill head from side to side by turning said drill string to change the radius of curvature of said inverted arcuate path.

13. A method for drilling underground an inverted arcuate path beneath an obstacle comprising the steps of: providing a drill string; providing a drill head having at least one cutting drill bit at the end of said drill string operative to cut independent of rotation of said drill string. said drill head having an angular axial alignment with respect to the axis of said drill string; thrusting the drill string angularly downward into the ground at an angle other than vertical; powering said drill head through fluid supplied under pressure through said drill string to a motor operatively connected to power said cutting drill bit; surveying the azimuth and declination of said drill string proximate said drill head at a plurality of intervals during said drilling; measuring the length of said drill string in the ground at the correspondent plurality of intervals from entrance into the earth at one side of said obstacle to exit from the earth at the other side of said obstacle whereby the path of said drill under said obstacle can be determined; and. varying the pressure of said drilling fluid through said drill string to control the radius of curvature of the inverted arcuate path.

14. The invention of claim 13 and including the step of varying said thrust of said drill string to change the radius of curvature of said inverted arcuate path.

15. The invention of claim 13 and including the step of changing the speed of said drill head to change the radius of curvature of said inverted arcuate path.

16. The invention of claim 13 and including the step of rocking said drill head from side to side by turning said drill string to change the radius of curvature of said inverted arcuate path.

17. The method as recited inclaim 13 wherein said powering step comprises increasing the pressure of drilling fluid through said drill string to increase the radius of curvature of said inverted arcuate path.

18. The invention of claim 13 and including the step of decreasing the pressure of drilling fluid through the drill string to decrease the radius of curvature of said inverted arcuate path.

19. A method for drilling underground an inverted arcuate path beneath an obstacle comprising the steps of: providing a drill string; providing a drill head having at least one cutting drill bit at the end of said drill string operative to cut independent of the rotation of said drill string. said drill head having an angular axial alignment with respect to the axis of said drill string; thrusting the drill string angularly downward into the ground at an angle other than vertical; powering said drill head through said drill string simultaneously with said powering and said thrusting step; surveying the azimuth and declination of said drill string proximate said drill head at a plurality of intervals during said drilling and measuring the length of said drill string in the ground at a correspondent plurality of intervals from entrance into the earth at one side of said obstacle to exit from the earth at the other side of said obstacle whereby the path of said drill under said obstacle can be determined; and. varying-the azimuth of the drill string about the axis of said drill string by rocking said drill head from side to side by turning said drill string to change the radius of curvature of the inverted arcuate path.

20. The invention of claim 19 and including the step of varying said thrust of said drill string to change the radius of curvature of said inverted arcuate path.

21. The invention of claim 19 and wherein said powering of said drill bit is provided by pumping fluid under pressure to a motor in said drill head operatively connected to said drill bit through-said drill string; and. varying said pressure of said fluid through said drill string to control the radius of curvature of said inverted arcuate path.

22. The invention of claim 19 and including the step of varying the speed of said drill bit to change the radius of curvature of said inverted arcuate path. 

1. A method for drilling underground an inverted arcuate path beneath an obstacle comprising the steps of: providing a drill string; providing a drill head having at least one cutting drill bit at the end of said drill string operative to cut independent of rotation of said drill string, said drill head having an angular axial alignment with respect to the axis of said drill string; thrusting the drill string angularly downward into the ground at an angle other than vertical; powering said drill bit through said drill string simultaneously with said thrusting step; surveying the azimuth and declination of said drill string proximate said drill head at a plurality of intervals during said drilling and measuring the length of said drill string in the ground at a correspondent plurality of intervals from entrance into the earth at one side of said obstacle to exit from the earth at the other side of said obstacle whereby the path of said drill under said obstacle can be determined; and, varying said thrust of said drill string to change the radius of curvature of said inverted arcuate path.
 1. A method for drilling underground an inverted arcuate path beneath an obstacle comprising the steps of: providing a drill string; providing a drill head having at least one cutting drill bit at the end of said drill string operative to cut independent of rotation of said drill string, said drill head having an angular axial alignment with respect to the axis of said drill string; thrusting the drill string angularly downward into the ground at an angle other than vertical; powering said drill bit through said drill string simultaneously with said thrusting step; surveying the azimuth and declination of said drill string proximate said drill head at a plurality of intervals during said drilling and measuring the length of said drill string in the ground at a correspondent plurality of intervals from entrance into the earth at one side of said obstacle to exit from the earth at the other side of said obstacle whereby the path of said drill under said obstacle can be determined; and, varying said thrust of said drill string to change the radius of curvature of said inverted arcuate path.
 2. A method as recited in claim 1 wherein said varying said thrust includes increasing the force on said drill string to decrease the radius of curvature of the inverted arcuate path.
 3. The method of claim 1 wherein said thrusting step includes decreasing the force on said drill string to increase the radius of curvature of the inverted arcuate path.
 4. The method of claim 1 and varying the speed of said drill head to change the radius of curvature of said inverted arcuate path.
 5. The method of claim 1 and wherein said powering step includes powering said drill head through said drill string by fluid supplied to a motor operatively connected to said drill bit, and including the step of varying the pressure of said fluid to said motor to change said radius of curvature.
 6. The invention of claim 1 and including the step of rocking said drill head from side to side by turning said drill string to change the radius of curvature of said inverted arcuate path.
 7. A method for drilling underground an inverted arcuate path beneath an obstacle comprising the steps of: providing a drill string; providing a drill head having at least one cutting drill bit at the end of said drill string operative to cut independent of rotation of said drill string; said drill head having an angular axial alignment with respect to the axis of said drill string; thrusting the drill string angularly downward into the ground at an angle other than vertical; powering said drill bit through said drill string simultaneously with said thrusting step; surveying the azimuth and declination of said drill string proximate said drill head at a plurality of intervals during said drilling and measuring the length of said drill string in the ground at a correspondent plurality of intervals from entrance into the earth at one side of said obstacle to exit from the eartH at the other side of said obstacle whereby the path of said drill under said obstacle can be determined; and, varying the speed of said drill bit to change the radius of curvature of said inverted arcuate path.
 8. A method as described in claim 7 wherein said varying of the speed of said drill bit includes the step of increasing the rotational speed of said drill bit to increase the radius of curvature of said inverted arcuate path.
 9. The method as described in claim 7 wherein said varying the speed of said drill bit includes the step of decreasing the rotational speed of said drill bit to decrease the radius of curvature of said inverted arcuate path.
 10. The invention of claim 7 and including the step of varying the thrust of said drill string to change the radius of curvature of said inverted arcuate path.
 11. The method of claim 7 and including the steps of powering said drill head by fluid communicated through said drill string to a motor operatively connected to said drill bit and controlling the radius of curvature of said inverted arcuate path by varying the pressure of said fluid.
 12. The invention of claim 7 and including the step of rocking said drill head from side to side by turning said drill string to change the radius of curvature of said inverted arcuate path.
 13. A method for drilling underground an inverted arcuate path beneath an obstacle comprising the steps of: providing a drill string; providing a drill head having at least one cutting drill bit at the end of said drill string operative to cut independent of rotation of said drill string, said drill head having an angular axial alignment with respect to the axis of said drill string; thrusting the drill string angularly downward into the ground at an angle other than vertical; powering said drill head through fluid supplied under pressure through said drill string to a motor operatively connected to power said cutting drill bit; surveying the azimuth and declination of said drill string proximate said drill head at a plurality of intervals during said drilling; measuring the length of said drill string in the ground at the correspondent plurality of intervals from entrance into the earth at one side of said obstacle to exit from the earth at the other side of said obstacle whereby the path of said drill under said obstacle can be determined; and, varying the pressure of said drilling fluid through said drill string to control the radius of curvature of the inverted arcuate path.
 14. The invention of claim 13 and including the step of varying said thrust of said drill string to change the radius of curvature of said inverted arcuate path.
 15. The invention of claim 13 and including the step of changing the speed of said drill head to change the radius of curvature of said inverted arcuate path.
 16. The invention of claim 13 and including the step of rocking said drill head from side to side by turning said drill string to change the radius of curvature of said inverted arcuate path.
 17. The method as recited in claim 13 wherein said powering step comprises increasing the pressure of drilling fluid through said drill string to increase the radius of curvature of said inverted arcuate path.
 18. The invention of claim 13 and including the step of decreasing the pressure of drilling fluid through the drill string to decrease the radius of curvature of said inverted arcuate path.
 19. A method for drilling underground an inverted arcuate path beneath an obstacle comprising the steps of: providing a drill string; providing a drill head having at least one cutting drill bit at the end of said drill string operative to cut independent of the rotation of said drill string, said drill head having an angular axial alignment with respect to the axis of said drill string; thrusting the drill string angularly downward into the ground at an angle other than vertical; powering said drill head through said drill string simultaneously with said powering and said thrusting step; survEying the azimuth and declination of said drill string proximate said drill head at a plurality of intervals during said drilling and measuring the length of said drill string in the ground at a correspondent plurality of intervals from entrance into the earth at one side of said obstacle to exit from the earth at the other side of said obstacle whereby the path of said drill under said obstacle can be determined; and, varying the azimuth of the drill string about the axis of said drill string by rocking said drill head from side to side by turning said drill string to change the radius of curvature of the inverted arcuate path.
 20. The invention of claim 19 and including the step of varying said thrust of said drill string to change the radius of curvature of said inverted arcuate path.
 21. The invention of claim 19 and wherein said powering of said drill bit is provided by pumping fluid under pressure to a motor in said drill head operatively connected to said drill bit through said drill string; and, varying said pressure of said fluid through said drill string to control the radius of curvature of said inverted arcuate path. 